Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 5 Section 3 Meiosis Chapter 5 Section 3 Meiosis Bellringer Objectives Write a sentence to describe each of the following terms: heredity, genotype, and phenotype. Note how genotype and phenotype are related, and how they are different. Is heredity necessarily a factor in both genotype and phenotype? Why or why not? • Explain the difference between mitosis and meiosis. Record your answers in your science journal. • Interpret a pedigree. Chapter menu • Describe how chromosomes determine sex. • Explain why sex-linked disorders occur in one sex more often than in the other. Resources Chapter menu Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 3 Meiosis Chapter 5 Vocabulary Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 Meiosis Asexual Reproduction • homologous chromosomes • meiosis • sex chromosome • pedigree • In asexual reproduction, only one parent cell is needed. The structures inside the cell are copied, and then the parent cell divides, making two exact copies. • This type of cell reproduction is called mitosis. Most of the cells in your body and most single-celled organisms reproduce this way. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 3 Meiosis Chapter 5 Section 3 Meiosis Sexual Reproduction Mitosis • In sexual reproduction, two parent cells (sex cells) join together to form offspring that are different from both parents. • Chromosomes that carry the same sets of genes are called homologous chromosomes. • Each sex cell has only one of the chromosomes from the homologous pair. Chapter menu Resources Chapter menu Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 3 Meiosis Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 3 Meiosis Sexual Reproduction The Steps of Meiosis • Sex cells are made during meiosis. • Meiosis is a copying process that produces cells with half the usual number of chromosomes. • Walter Sutton studied meiosis in sperm cells in grasshoppers. • During meiosis, chromosomes are copied once, and then the nucleus divides twice. • The resulting sex cells (sperm and eggs) have half the number of chromosomes of a normal body cell. • Using his observations and his knowledge of Mendel’s work, Sutton proposed that: Genes are located on chromosomes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 3 Meiosis Chapter menu Chapter 5 Resources Chapter menu Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 3 Meiosis Section 3 Meiosis Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 3 Meiosis Meiosis and Mendel • The steps of meiosis explain Mendel’s results. The following slide shows what happens to a pair of homologous chromosomes during meiosis and fertilization. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 3 Meiosis Chapter 5 Section 3 Meiosis Meiosis and Mendel Meiosis and Mendel •The genes for certain disorders, such as colorblindness, are carried on the X chromosome. • Sex Chromosomes carry genes that determine sex. •Genetic counselors use pedigrees to trace traits through generations of a family. These diagrams can often predict if a person is a carrier of a hereditary disease. • Human females have two X chromosomes. • Human males have one X chromosome and one Y chromosome. • In selective breeding, organisms with desirable characteristics are mated. Chapter menu Resources Chapter menu Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 3 Meiosis Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 3 Meiosis Section Summary • In mitosis, chromosomes are copied once, and then the nucleus divides once. In meiosis, chromosomes are copied once, and then the nucleus divides twice. • The process of meiosis produces sex cells, which have half the number of chromosomes. These two halves combine during reproduction. • In humans, females have two X chromosomes. So, each egg contains one X chromosome. Males have both an X and a Y chromosome. So, each sperm cell contains either an X or a Y chromosome. A pedigree is a diagram that shows the occurrences of genetic traits in several generations of a family. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. • Sex-linked disorders occur in males more often than in females. Colorblindness and hemophilia are examples of sex-linked disorders. • A pedigree is a diagram used to trace a trait through many generations of a family. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.